A circuit breaker is a packaged device, which serves to interrupt electrical current flow in an electrical circuit path upon the occurrence of an overcurrent in the circuit path. Typically, the circuit breaker provides a form of temporal averaging of the current, such that noise or transients do not trigger the breaker, while significant overcurrents rapidly trip the breaker. In addition, circuit breakers typically have a user interface comprising a handle, depressible surface, or toggle, to provide manual control over the breaker and possible visible or palpable indication of state. The typical circuit breaker has four main components: the housing, the mechanism that operates the switching contacts, the current sensor, and the user interface.
Typically, the breaker is arranged with the user interface elements on a face of the breaker, with the electrical interface on an opposite side of the housing. Inside the housing, the contact arm, and collapsible toggle linkage mechanism for breaking the circuit, are generally placed adjacent to the current sensor, e.g., particularly a magnetohydrodynamic coil.
The contact arm of a circuit breaker has a relatively strong spring, to assure rapid and reliable breakage of the circuit after a trip event. The trip element and toggle linkage are connected through a pivoting arm or armature, which, when activated, triggers a collapse of the toggle linkage, resulting in a rapid opening of the circuit. When the overcurrent occurs, the external toggle handle will normally return from the ON position to the OFF position.
Because the user interface must apply a significant force to place the contact arm in the conducting position against the spring force, it is typically placed immediately on top of the contact arm and toggle mechanism, with a direct transfer of mechanical force. For example, the handle of a circuit breaker pivots and applies a force, through the collapsible toggle linkage on the contact arm.
The trip mechanism, on the other hand, applies a much lower force, which is multiplied by the toggle linkage, to trigger the collapse of the toggle arm and swing of the contact arm. For efficiency, the sensing mechanism has traditionally been mounted on the same frame, opposite to the contact arm. This arrangement is spatially compact, and provides relatively short internal electrical paths for the current flow.
This arrangement places the magnetohydrodynamic coil, the toggle mechanism, and the arc chute in series, and together they determine the total height of the circuit breaker. Typically, the proportions of these three elements are 30% for the magnetohydrodynamic coil, 40-45% for the toggle mechanism, and 25-30% for the arc chute.
One popular circuit breaker design has a total housing height of about 2 inches, with a toggle mechanism occupying about 0.8″. In communications equipment applications, equipment is generally housed in equipment racks complying with EIA-310-D, which defines a cabinet height in multiples of about 1.75 inches. A 2 inch breaker will therefore not fit with its height aligned with the cabinet height in a 1U cabinet. Likewise, for larger circuit breaker sizes, similar issues may arise leading to an inefficient utilization of cabinet height.
For a given electrical rating, which is strongly influenced by the size of the contact mechanism and clearances, the height dimension of the breaker has traditionally thus been limited in its minimum size. Thus, the art requires a circuit breaker design having a reduced height dimension with comparable electrical ratings to traditional designs.